Recently, a leukocyte-independent form of complement (C')-mediated glomerular injury was defined in passive Heymann nephritis (PHN), a rat model that closely resembles human membranous nephropathy which is a common cause of nephrotic syndrome in adults. While further observations have suggested a role for the C5b-9 membrane attack complex (MAC) in this and other forms of tissue injury, this has not been conclusively shown. Variants of PHN and a recently developed model of antibody (Ab)-directed, C'-mediated glomerular injury in the isolated perfused rat kidney (IPRK) will be used to further study this unique form of tissue injury. Kidneys that contain an antigen planted in the subepithelial space are perfused in vitro with a cell-free perfusate containing C'-fixing Ab and various sources of C'=replete and C'-deficient sera. The effects on glomerular function are oserved for up to two hours. With the aid of this model, definitive evidence of a functional role for the MAC will be sought using sera deficient in C6 and C8. Additional studies will examine: the possible role of intermediary systems; C'-mediated alterations in glomerular sieving properties, GBM charge residues, and glomerular podocyte morphology; and localization of the MAC by immunohistological and ultrastructural techniques. The role of the MAC will also be examined in vivo by depleting rats of C8 with a specific antiserum. Similar observations in the IPRK and in vivo will also be made with antiglomerular basement membrane (GBM) antibody. Also to be examined in the IPRK are: a) a potential relationship between immunopathogenetic events, locally-derived vasoactive hormones and disordered renal hemodynamics in PHN; and b) the influence of hemodynamic factors on the binding of Abs to glomerular antigens. An erythrocyte-perfused IPRK, in which hemodynamic variables approach physiological values, will be used for these studies. In addition, the relationship between the density of glomerular antigens and the abilities of their respective antibodies to fix C' and induce glomerular injury will be explored. Sheep antisera to laminin and rat GBM and quantitative in vivo and in vitro glomerular binding techniques will be used for this purpose. The proposed studies will further the long term goals of Investigator, which are to comprehensively analyze the factors that influence Ab deposition in glomeruli and the ways in which such Abs interact with C' and other mediators to induce glomerular injury.